Field of the Invention
The invention relates to a device for recording or determining the instant at which injection starts in an injection valve of an internal combustion engine, having a differentiating device to which current through the injection valve is supplied and which emits an output signal.
Such a device is known, for example, from German Patent DE 28 05 175, corresponding to U.S. Pat. No. 4,228,680. In that device, a mechanical/electrical motion pick-up is provided which generates an electrical signal corresponding to a lift motion of the injection valve. The signal is supplied in differentiated form to a threshold value switch having a response which marks the start of injection.
Due to the differentiation of the pick-up signal, the instant at which injection starts can be recognized more rapidly and more accurately than it would be if the non-differentiated pick-up signal were inspected.
The device requires such a motion pick-up for each injection valve being inspected. However, due to the trend towards smaller and smaller injection valves, it is becoming increasingly more difficult and expensive to provide such pick-ups.
A device for checking a magnetic valve for the injection system of an internal combustion engine is known from Published Japanese Abstract No. 1-105084. Changes in the shape of the curve of the triggering current are used to recognize erroneous functioning of that valve and are differentiated for easier analysis of the signal.